Triazine herbicide contamination of Tasmanian streams: Sources, concentrations and effects on biota

Abstract

Concentrations of the triazine herbicides atrazine, simazine, cyanazine, metribuzin and propazine were determined in streams draining forestry and agricultural catchments in Tasmania, Australia, between 1989 and 1992. Atrazine and simazine were used extensively by the forestry industry in a winter spraying programme, and applications of the other herbicides occurred in cropped agricultural catchments during spring and summer. Of 29 streams sampled intensively for triazines, 20 contained detectable residues. Median contaminations over all samples were 2.85, 1.05, <0.05, <0.05 and <0.05 µg L^-1 for atrazine, simazine, cyanazine, metribuzin and propazine, respectively. All herbicide concentrations ranged over several orders of magnitude up to 53 mg L^-1, with atrazine and simazine having significantly higher concentrations than the others. Atrazine concentrations were examined in streams draining forestry plantations for periods of up to two years. A decline in concentration was observed with time, but this was strongly influenced by rainfall events. Atrazine contamination from single spraying events persisted at a low level for up to 16 months. Contamination of Big Creek with atrazine to 22µg L^-1 after aerial spraying led to an increase in stream invertebrate drift only on the day of spraying and to a short-term increase in movement of brown trout. On examination of biological effects of triazines in surface waters reported in the literature, it was concluded that the observed frequent contamination of Tasmanian streams with triazines may cause occasional minor short-term disturbance to stream communities.